Brillouin scattering in planar waveguides

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Abstract
Brillouin spectra have been measured in silica-titania planar waveguides of different thicknesses, obtained by radio-frequency sputtering. The laser beam was coupled to the waveguide with a prism and the scattered light was collected from the front surface. The spectra, which are different for excitation in the different modes of the waveguide, are accounted for by a model that considers the space distribution of the exciting field. This allows measuring the sound velocities in the film. The role of the finite thickness of the planar waveguide is discussed.